Fair Value Measurements (Details) - USD ($)	Sep. 30, 2019	Mar. 31, 2019
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total assets	$ 143,614,000	$ 126,133,000
Total liabilities	0	0
Money market funds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	53,000	83,000
Commercial paper
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	130,953,000	126,050,000
Corporate bonds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Corporate bonds	12,608,000
Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total assets	53,000	83,000
Level 1 | Money market funds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	53,000	83,000
Level 1 | Commercial paper
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	0	0
Level 1 | Corporate bonds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Corporate bonds	0
Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total assets	143,561,000	126,050,000
Level 2 | Money market funds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	0	0
Level 2 | Commercial paper
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	130,953,000	126,050,000
Level 2 | Corporate bonds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Corporate bonds	12,608,000
Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total assets	0	0
Level 3 | Money market funds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	0	0
Level 3 | Commercial paper
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	0	$ 0
Level 3 | Corporate bonds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Corporate bonds	$ 0